On the way to a better performance prediction for small-diameter hard rock TBMs

Small diameter tunneling in hard rock gets increasingly widespread due to the surge of renewables energies and the need for new and longer utility tunnels. The large variety in this small diameter range in hard rock includes different TBM types, cutterhead designs, cutter types and most notably geotechnical conditions. Predicting the advance rate for such project conditions in hard rock is an important factor in tunnel project planning and execution. Data from more than 35 small diameter hard rock tunneling pipe jacking and segment lining projects has been compiled and analyzed. Our analysis showed that the achieved performance for such projects varies considerably from the prediction with industry-standard penetration models. This paper will give an insight into the wide variability of small diameter hard rock tunneling and the associated challenges in performance prediction.